Purification of amine reaction mixtures



Patented Nov. 26, 1946 c, 4

STATE PURIFICATION ions. F. Olin,

, Sharnles, Chem ca a,v corporation of-Delaware F AMINE REACTIONMIXTURES Grosse Ile, Mich., assignor to Bh ad ph a, Pa, a

No Drawing. ApplicationiMay 5, 1944,

Serial No. 534,353

G-Claims, (01. 260-585) The present invention. pertainstothepurification of crude reaction mixtures resulting fromammonationereduction of, aliphatic aldehydes. or ketones by reactionthereof with ammonia or amines, and hydrogen in the presence of ahydrogenation catalyst. Amination reactions of this general type arewell-known in thear-t, and have been performed both in the liquid and inthe vapor phase, as illustrated respectively by the article by- Mignonacin Comptes Rendus, volume 172, page 223, and the copending applicationof John F. Olin- & James F. McKenna, Serial Number 428,548,filed-January 28, 1942. While the selective production of mono-,diandtri-alkyl aminesmay, to a large extent, be controlled byappropriate control of the proportions of reactants employed, it isinevitable that, in a process of this kind; a mixtureof the three amineswill .be obtained'in' use of ammonia as the aminating-agentyor a mixtureof diand tri-alkyl amines obtained in cases in which liberate amono-aliphatic amine is used 'as the aminating agent. In the majority'ofcases of use of these amines, the user wishes to employ one of the threeamines resulting from the reaction to the virtual exclusion of the othertwo. It is also necessary that-the amines or mixture of amines obtainedfrom the reaction be separated'from other contaminating;impurities, suchas nitriles,

carbamates, imines, carbon dioxide, ammonia, aldehydes or ketones,alcohols, etc. The removal of certain of these impurities presents aproblem, not only because of the fact that the impurities areundesirable in the finished products, but also because of the fact thatthe presence ofthe impurities in the reaction mixture renders, theproblem of separation'of the amines from each other more difiicult.Whilethe invention may be applied in purification of reaction mixturesobtained by ammonation-reduction of either aldehydes or ketonesregardless of carbon content, it is. especially, recommended fortreatment of such mixtures obtained from aldehydes. Problemsencounteredin purification of amine-containingreaction mixtures fromammonation-reduction of aldehydes containing from two to six carbonatoms can be solved with particular advantageby practice of theinvention. Ketones of from three to six carbon atoms are also withinthe. referred range of the invention. a

The present invention restslupon the discovery mixtures such as thosedis- I V thoroughly .mixed with an aqueous solution of an inorganicbase, and the amines contained in the reaction mixture are that, whenreaction cussed, above are thereafter removed by distillation from theresulting mixture, the operations of separating the respective aminesfrom each other and from impurities is. greatly facilitated. While I donot wish to belimited by any theoretical reasoning concerningresultsattained by the. practice' of the. invention, itis believed that thetreatment ofuthe crude reaction mixture by an inorganic base resultsire-reactions by which certain-constituents of the amine-containingreaction'mlx-: ture undergoa chemical change which'resultsi in theirconversion into=non-volatile, water-soluble; salts, and that the removalof these constituents in the form of an aqueous solution permits theremaining constituents of the reaction mixture to .be separated'fromeach other with greater facility. The basic treatment also serves to thedesired amines from chemical com-' bination in other constituents of themixture, suchas carbamates and imines and thus to improve the yieldwhile facilitating eificient distillation. When reaction -mixturescontaining carbamates have been distilled, this has resulted in pluggingdistillation equipment and also in inefficient separation of the aminesfrom each other. By the preliminary treatment of the present invention,.both of these difiiculties. are avoidedv The process of the presentinvention may be accomplished either by batch or continuous operation.If it is accomplished by batch operation, the crude amine-containingreaction mixture (after removal of fixed gases, if desired) may be mixedwith an aqueous basic solution for a sufficient" length of time toeffect solution in the aqueous phase of reaction'products of'the'baseupon constituents of the reaction mixture. This may be accomplished atatmospheric or super-- the amine-containing reaction mixture willcontain, a suificient amount of water to dissolve the added base, and insuch case the base may be added in solid form.

After the desired contact between the crude reaction mixture and thebasic solution is accomplished, the constituents-of the reaction mixturewhich are notconverted into non-volatile comp unds; bit t a m nt th.the. b se are. rem v d the reaction by which impurities separatelycondensing and collecting the tween and from the aqueous phase bydistillation. This may be accomplished by fractional distillation fromthe aqueous phase; 1. e., by distilling and separate constituents of thereaction mixture; or it may be accomplished by distilling overhead allof the constituents of the mixture resulting from the treatment with thebasic solution which are more volatile than the basic solution itself,and thereafter subjecting the mixture of organic constituents soobtained in the distillate to a separate fractionation by distillation.

The present invention may be very effectively practiced in a continuousmanner by mixing the crude amine reaction mixture with the aqueous basicsolution during continuous flow of the crude reaction mixture, andsubjecting the resulting mixture formed by addition of the base todistillation in the same apparatus in which the mixplace, or in separateapparaing operation takes tus. If such an operation is performed, it mayinvolve concurrent flow of the amine mixture and basic solution to thezone of separation, or counter-current fiow of the basic solution withrespect to the amine-containing mixture with separation beingaccomplished immediately following the counter-current treatment. 'Thus,for example, the amine-containing mixture may be introduced into afractionating column under pressure and temperature conditions at whichit is maintained in vapor phase, and the basic solutionmay be introducedinto an upper part of the same column in liquid phase. Such an operationresults 'in intimate contactv between the basic solution and theamine-containing mixture, with prompt reaction to form non-volatilesalts, which are dissolved in the aqueous phase, as discussed above, theaqueous phase passing downwardly through the column at the same timethat the remaining amine-containing reaction mixture is removed overheadas a distillate.

In case of practice of the invention on a reaction mixture obtained by acontinuous ammonation-reduction (amination) reaction, the operation oftreatment of the reaction mixture with a base is also preferablyperformed continuously, and is preferably accomplished by introductionof the amination reaction mixture continuously into the lower part of acolumn while introducing an aqueous basic solution into the upper partof this same column. In case of this type of operation, the basicsolution is preferably relatively dilute, caustic soda solutions ofbeconcentration being preferred, although a considerably wider range ispermissible. By using relatively dilute basic solutions in practice ofthe process continuously, the difliculty of precipitation of reactionproducts in the extraction column is avoided.

Part or all of the fixed gases of the reaction mixture may be removedbefore the treatment with the base and subsequent distillation, and whenthe invention is practiced by accomplishing the basic treatment inbatch, this sequence is ordinarily used. In case of batch operation,much more concentrated solutions may be-used than in case of continuousoperation, and the invention may even by practiced by introducing thebase as a solid in the case of batch operation, since the reactionmixture will ordinarily contain suiiicient water to dissolve the addedbase, as pointed out above.

Example I drogen through a heated reaction tube was first vented,through a column carrying an ammonia reflux, to remove hydrogen and mostof the ammonia of the reaction mixture. 120 grams of flake sodiumhydroxide were added to 938.5 grams of the residual crude reactionmixture, containing the three ethyl amines and various impurities. Theresulting mixture was shaken vigorously, causing the added sodiumhydroxide to dissolve in the water contained in the crude reactionmixture. The resulting mixture was then fractionally distilled, with theresult that 359 grams of monoethyl amine, 139-grams of diethyl amine and230 grams of wet triethyl amine (consisting of an azeotropic mixture oftriethyl amine and water) were obtained. This distillation wasaccomplished Without any difliculty, and the respective amines wereobtained as very sharply defined fractions. When an attempt was made toseparate an equivalent reaction mixture without the preliminary sodiumhydroxide treatment, difficulty was encountered both in connection withthe purity of the respective amine fractions, and because of plugging ofthe distillation equipment.

' Example II A crude reaction mixture formed by the reac-' tion ofacetaldehyde with ammonia and hydrogen by continuous vapor phaseamination, was cooled to liquefy the ethyl amines and the higher boilingproducts and also part of the ammonia. Hydrogen, hydrocarbon and someammonia were separated from the reaction mixture, and the remainingliquid products were passed into the central portion of a scrubbingcolumn maintained at a temperature of about 100 C. An aqueous sodiumhydroxide solution of 10% concentration was run into the column at atemperature of 125 C., and a pressure of about -75 pounds per squareinch was maintained on the system during performance of the scrubbingoperation by flow of the reaction mixture in counter-current directionto the ascending stream of gases to perform the scrubbing operation. Theliquid leaving the bottom of the scrubberconsisted essentially of water,sodium carbonate and. sodium acetate, while the volatile organicsubstances and ammonia passed overhead. Upon subsequent fractionation ofthe overhead fraction, sharp separations between the respective amineswere obtained. Y

Example III A crude reaction mixture resulting from passage ofbutyraldehyde together with a molecular excess of hydrogen and ammoniaover a catalyst consisting of pelleted nickel on kieselguhr at atemperature of approximately C. was mixed with 10% of its weight of 50%NaOH solution and fractionally distilled with no appearance ofinterfering solid precipitated material in the column or condenser.Monobutyl amine of high titre was obtained directly inthisfractionation. Dibutyl amine and tributyl amine were distilledoverhead as azeotropic mixtures with Water and separated from the waterby decantation. The water was returned continuously to the pot of thedistillation column until all of the di-' and tri-butyl amines had beenremoved. The mixture of diand tri-butyl amines obtained in this way wasdried by treatment with a 50% 'NaOH solution. The amine layercontainingthe dry diand tri-butyl amines was then fractionated to-separate these amines from each other, and these respective amines wereobtained in a'hlgh degree of purity.

radicals as discusscd'above, it can action mixtures resulting While theinvention has been especially useful in treatment of reaction mixturescontaining amines of from 2 to 6 carbon atoms in their alkyl also bepracticed in treatment of crude methyl amine reaction mixtures obtainedby ammonation-reduction of formaldehyde, and by treatment of reactionmixtures containing amines of more than six carbon atoms in their alkylradicals.

Various modifications are possiblewithin the scope of the invention, andI do not therefore wish to be limited except by the scope of thefollowing claims. a

I claim:

1. In the purification of amine-containing reaction mixtures resultingfrom reaction of aliphatic aldehydes with aminating agents and hydrogen,the process comprising mixing the crude reaction mixture containing theamine bases with an aqueous solution of an alkali metal hydroxide andsubsequently separating the amine bases from the resulting aqueoussolution by distilla- 'tion.

2. In the purification of amine-containing reaction mixtures resultingfrom reaction of aliphatic aldehydes with aminating agents and hydrogen,the process comprising mixing the crude reaction mixture containing theamine bases with an aqueous solution of an inorganic base andsubsequently separating the amine bases from the resulting aqueoussolution by distillation.

3. In the purification of amine-containing rey from reaction ofalialdehydes with aminating' agents and hydrogen, the process comprisingmixing the crude reaction mixture containing the amine bases with anaqueous solution of an inorganic base and subphatic 6 4 'sequentlyseparating the amine bases from the resulting aqueous solution anddistilling said amines to separate them from each other.

4. In the purification of amine-containing reaction mixtures resultingfrom reaction of aliphatic aldehydes containing from 2 to 6 carbon atomswith aminating agents and hydrogen, the process comprising mixing thecrude reaction mixture containing the amine bases with an aqueoussolution of an inorganic base and subsequently separating the aminebases from the resulting aqueous solution by distillation.

5. In the purification of ethyl amine-containing reaction mixturesresulting from reaction of acetaldehyde with aminating agents andhydrogen, the process comprising passing the crude reaction mixtureupwardly in vapor phase through a distillation column in counter-currentrelationship to an aqueous solution of an inorganic base passeddownwardly through said column and removing the resulting aqueoussolutiondownwardly from a lower portion of the column 'while theamine-containing mixture is passed upwardly in vapor phase through saidcolumn.

6-. In the purification of amine containing reaction mixtures resultingfrom reaction of a carms solution by distillation.

bonyl compound chosen from the class consisting of aliphatic aldehydesand ketones with aminating agents and hydrogen, the process comprisingmixing the crude reaction mixture containing the amine bases with anaqueous solution of an inorganic base and subsequently separating theamine bases from the resulting aque- JOHN F. OLIN.

